A novel thermophilic methane-oxidising γ-Proteobacterium

A novel thermophilic methane-oxidising bacterium was isolated from underground hot springs in Hungary. Strain HB grew on methane at up to 72 degrees C, the highest recorded growth temperature for a methanotroph. 16S rDNA phylogenetic analysis showed that strain HB was the first known representative of a novel, deep-branching group of the gamma-Proteobacteria quite distinct from extant methanotrophs. The nucleotide sequence of pmoA, encoding particulate methane monooxygenase, was determined for this novel thermophile. Sequence comparison showed that the methane monooxygenase of this strain was most closely related to that of Methylocaldum and Methylococcus species. Particulate methane monooxygenase gene fragments having a high degree of identity to that of pmoA from strain HB were amplified by PCR from DNA isolated from thermophilic methane-oxidising enrichments inoculated with hot spring samples (55-70 degrees C) from Japan, suggesting that this novel genus, for which we informally suggest the name 'Methylothermus', is widespread in thermophilic environments. (C) 1999 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.